An interface with a linear quadrupole ion guide for an electrospray-ion trap mass spectrometer system

A new ion sampling interface for an electrospray ionization 3D ion trap mas s spectrometer system is described. The interface uses linear rf quadrupole s as ion guides and ion traps to enhance the performance of the 3D trap. Tr apping ions in the linear quadrupoles is demonstrated to improve the duty c ycle of the system. Dipolar excitation of ions trapped in a linear quadrupo le is used to eject unwanted ions, A resolution of ejection of up to 254 is demonstrated for protonated reserpine ions (m/z 609.3), A composite wavefo rm with a notch in frequency space is used to eject a wide range of matrix ions and to isolate trace analyte ions in a linear quadrupole before ions a re injected into the 3D trap. This is useful to overcome space charge probl ems in the 3D trap caused by excess matrix ions. For trace reserpine in a 5 00-fold molar excess of poly(propylene glycol) (PPG), it is demonstrated th at the resolution and sensitivity of the 3D trap can be increased dramatica lly with ejection of the excess PPG matrix ions. In comparison to ejection of matrix ions in the 3D trap with a similar broad-band waveform, a ii-fold increase in sensitivity with a 7 times shorter acquisition time was achiev ed.